Solvent extraction operation



Oct. 8, 1940. Q e. T. ATKINS. JR 2,215,932

SOLVENT EXTRACT ION OPERAT I 0N Filed Feb. 27, 1939 2 Sheets-Sheet 1 PE-EXTRAC' T/ON EXTRA 07-10 rcwz n.

RAF'F'l/VATE LUBE OIL.

.D/sr/u A rmy .D/sru I. A TE 0! 7- PHAT/VOL EXTRACT LINE 0 fw 5W Patented Oct. 8, 1940 SOLVENT EXTRACTION.

TERATTON George "I". Atkins, J12, Highlands, Tex.,tissignor to Standard Oil Develop poration of Delaware 1 C nv rt,

The present invention relates tothe art of -sole vent treating oils. The invention is concerned with a method ofseparating oils into their rela- .tively more aromatic or hydrogenepoor constituents and into their relatively more parafiinic or hydrogen-rich constituents by means of selective solvents which have a preferential selectivity for the more aromatic or hydrogen-poor constituents as compared to the relatively more par'aflinic or hydrogen-rich constituents. The invention es.- pecially relates to an improved process of economically recovering and purifying said selective solvent without the necessity of distilling the same. i I

In accordance with the present process, a feed oil, preferably a petroleum oil, is separated into three fractions, the first of which comprises la major quantity of highlyaromatic components of greatest solubility in the primary solvent,.the f second of which'comprisesa major quantity of aromatic components of intermediate solubility in theprimary solvent, while the third comprises a' majorfquantity of parafiinic components of lowest solubility in the primary solvent. The first fraction comprising highly aromatic components is removed from the feed oil in a pretreating extraction zone by means of undistilled pri mary solvent. The second fraction comprising aromatic components of intermediate solubility in the primary solvent is removed from thetprei treated feed oil in a main treating zone by means of the primary solvent, the major portion of which has been recovered from the oil by re-extraction in a secondary treater with asecondary solvent having a preferential selectivity for the extract as compared to the primary solvent; The third fraction relatively paraflinic in nature is recovered from the main treater after'a final extraction with a minor proportion of distilled primary solvent.

It is well known intheart to segregate petroleum oils into relatively moreparafiinic or relatively hydrogen-rich fractions and into relatively. more aromatic or relatively hydrogen-poor fracsolvent mixtures. I complished by means of selectivesolvents. of the class which have a preferential selectivity forthe more aromatic type compounds as compared to the relatively more parafilnictype compounds. Solvents of this class are, for example, phenol, furfural, aniline, nitrobenzene, beta beta dichlor diethyl ether, and the like. These solvents are also employed together as. well as incombination M with other substances, as for example, substances tions by means of various selective solvents or 1 The separation is usually ac-;

of class ofliquid normally gaseous hydrocarbonssuchas ethane, propane, butane, and the i like. It is.a1so known to use substances which haveuthe ability to modify the selectivity and solvent power of the solvent, as for example, water, alcohols glycols, and the like. The solvent, .or solvent mixture, andthe feed oil may be contacted I in any suitableimanner, as for example, by a multi-stageforbatch operation; The usual processQh WeVerQisto contact the oil and solvent ina fthe lig hter component, usually the oil, is introjduce'd, in' the bottom or the tower and the heavier component, usuallysthe solvent, is introduced in the top portion of thetowerg These phases flow countercurrently, intimately contacting each iotherfusuailly. being assisted. by various contactingfand distributing'means. The extraction op- ;erations are'icarried out under; various temperatlll fdal ld pressure conditions depending upon the material beingtreated, the volume of solvent used- -pervbluiiaeof oil being treated, aswell as upon the quari tity and qualityof the products desired. In general; atmospheric pressure and a tempera- 'ture between .the melting point of the solvent and thetemperature at which complete miscibility occurs between the oil and solvent are employed. *In theseprocesses, the usual procedure is to 'separate the solvent rich or extract phase from 'the"solvent-poorer raftinate phase and to recover sheet from-the solvent from the respective phases by di'stillation. This has not been entirely satisfactorysihce the specific heat and heat or vaporization of desirable solvents are relatively high',thu"s'] resulting in considerable heat loss and materially increasing the cost of operation. Fur"- thermore, distillation causes a mechanical solcountercurrent tower treating operation in which vent loss as well asa loss due to thermal degradation-of solvent; This is significant when it is con- :sidered that solvents having.v desirable selective characteristics are relativelyexpensive.

Various;processeshave been directedto the recovery of. the selective solvent from the I'GSDBC? .tiveraflinate and extract phases in a more ecu-,- nomical and (practical manner. For example, it is known in the art tore-extract a solvent ex+ tractwith: a Lsecondarysolvent, as for example,

.naphtha,,in-=order toremove the extract-from -theflprimary solvent. 1 The secondary solvent con tainingthe extract is then separated from the extract bylpdistillation. This process effects considerable economies since the primary solvent "lossfl'is substantially decreased. The distillation cost;,,is;;likewi se decreased since the latent heat gofthe secondarygsolvent is less than the latent in an eificient and practical manner.

I have now discovered a process by which it is possible to separate a petroleum oil into relatively more parafiinic fractions and intorelatively more aromatic fractions by means of a primary selective solvent and to re-extractthe separated solvent extract phase with a secondary solvent specifically to Figure 1 for purposes of illustration, it is assumed that-the primary solvent is phenol, that the'feed'oil is a'petroleum lubricating oil distillate, andthat the secondary solventis a close out naphtha containing minimum amounts of those hydrocarbon'components which are especially 'solublejin a primarysolvent and having an average'b'o'iling point in the range from about 350 F. to 400 F. and which is termed Paracyclo. The petroleum oil charge stock is introduced into pretreater tower I by means of feed line 2. This feed oil flows upwardly through tower l intimately contacting a relatively small percentage of. undistilled' total phenol which is introduced into tower l by means of feed line 3. Tower 1 contains suitable distributing and contacting means. Conditions on tower l are maintained to secure the formation of a solvent extract phase and a raflinate phase. The solvent extract phase isremoved from tOWCIj Ifb-Y means of line 4 and contains the most soluble components of the more aromatic type materials present in the original feed oil and a small percentage of the total primary solvent used in the process.

.This small percentage oftotal phenol-is removed from the pretreater extract by means of distillation equipment 5. The distilled phenol is removed from distillation unit 5 by means of line I5 while the highly aromatic fraction is removed by means of line l6.

The undissolved oil phase is removed from tower I by means of line 6 and introduced near the bottom of the. main extraction tower 1. The feed oil phase to tower T flows upwardly through the tower and contacts the major quantity of total undistilled phenol which is introduced into tower 'l-by means of line 8. Tower 8. contains Suitable distributing and contacting means. The rafiinate phase is removed from tower I by means of line 9 and treated in a manner to remove the raiiinate oil from the small amount of solvent. This is preferably accomplished by distillation.

The extract dissolved in the primary solvent is The of line l2 and which has a preferential selectivity for the extract as compared to the primary solvent. The secondary solvent containing the extract oil is removed from tower H by means of line l3 and the undistilled recovered phenol is removed from tower II by means of line I4. The

major proportion of the undistilled recovered phenol is introduced into tower l by means of line 8 while the minor proportion of the recovered phenol is introduced into tower l by means of line 3.

A further modification of my invention may be seen by reference to Figure 2. For the purpose of illustration; it is assumed that the feed oil is a lubricating oil distillate, the primary solvent is phenol, and that the secondary solvent is paracyclo. The lubricating oil is introduced into tower 20 by means of feed line 2 I. The feed oil flows upwardly through tower 2i) and contacts a small percentage of undistilled phenol which is introduced into tower 20 by means of line 22. It is to be understood that the selectivity and solvent power of the primary solvent may be modified by the introduction of a solvent modifying agent. Thus, for example, the selectivity of the phenol may be modified by the introduction of water, preferably introduced at more than one stage, by means of line 23. Conditions are maintained on tower 2D to secure the formation of a rafiinate phase and a solvent extract phase. The pretreater solvent extract consisting of a minor proportion of the undistilled solvent and the greater proportion of those most highly aromatic type materials present in the feed oil is removed from tower 29 by means of line 2 1 and introduced into pretreater extract stripper 25 in which phenol is removed from the extract by distillation. The pretreater extract is removed from pretreater extract stripper 25 by means of line 28 and the distilled phenol by means of line 46.

The undissolved oil phase from tower 2B is removed by means of line 21 and introduced in the lower part of tower 28. The feed oil to tower 28 flows upwardly through the tower and contacts in the initial stages the major proportion of total undistilled phenol which is introduced into tower .28 by means of line 29. Water or a similar solvent modifying agent may be injected into tower 28 by means of line 30. In the latter stages the up-flowing feed oil contacts distilled phenol which is introduced into tower 28 by means of line 3!. The raffinate phase is removed from tower 28 by means of line 32 and taken to rafflnate stripper 33 in which the phenol is separated from the rafiinate by distillation. The solvent free raflinate is removed from raftinate stripper 33 by means of line 3,4 and the distilled phenol by means of line 15. The solvent extract from tower 28 is removed by means of line 35 and is introduced in the top of-re-extraction tower 36. Prior to entry into tower 36, the solvent extract from tower 28 may be cooled by means of cooler 44 or may be diluted with water introduced into line 35 by means of line 45, or both, for the purpose of reducing the solubility of extract oil in the primary solvent.

The primary solvent phase flows downwardly through tower 36 and contacts up-flowing paracyclo which is introduced into tower 36 by means of line 31. The paracyclo extracts the oil from the phenol and is removed as secondary solvent extract phase by means of line 38. The secondary solvent extract phase is taken to extract stripper 39 in which theisec'ondary solvent is separated frorn the extract;,-preferably by distillation. e'solvent-free"extract is removed from extract stripper 39 by means of line 41 and the distilled solvent'is removed by means of line 46. The maj or proportion of undistilled phenol is removed from tower36 by means of line 40 and dried tothe desired extent in drier4l. A minor proportion of the totalphenol is removed from drier 4| and introducedinto pro-treater tower 20 by means of line 22. The major proportion of the total phenol is introduced into extraction tower 28 by means of line 29. Phenolic water, recovered in drier 4|, is preferably introduced into towers 20 and 28 by means of lines 23 and respectively. 1

} Distilled phenol from the respective strippers 25,",and3 3 and 39 is condensed and cooled and allowed to layer in phenol storage 43. The layer of distilldphenol is returned to the top of tower ill} by meansof line 3]. .Normally, it is preferred t6 return an or the undi'stilled phenol from drier 4i to tower 28 by ,meansoflin'e 29 and to supply pretreater tower 20 with a solvent phase containing dissolved oil fractions of intermediate solubility through line 42 and 22from tower 28. This solvent phase is preferably removed from tower 28 from a point near the pretreater oil feed inlet to tower 28.

The process of the present invention may be widelyvaried. It is preferred to use a primary solventselected from the classof solvents which have a preferential selectivity for the relatively more aromatic or. hydrogen-poor compounds as compared to the relatively more paraffinic or hydrogen-rich compounds. Primary solvents of this class are, for example, furfural, aniline, nitrobenzene, beta beta dichlordiethyl ether, sulfur dioxide, and the like, or mixtures of these. The preferred primary solvent is phenol, the selectivity of which may be modified by means of a solvent modifying agent, such as water, which is preferably introduced at more than one stage. The secondary solvent suitable for re-extracting the primary solvent extract may be any solvent which has a preferential selectivity for, the extract as compared to the primary solvent. Preferred secondary solvents are highly parafiinic materials boiling in the range from about 200 F. to 600 F. and having amid boiling point in the range from about ,350;F. to 400 F. The

preferred secondary solvents are those which of the products desired. For example, when employing phenol as the primary solvent, it is pre ferred to use atmospheric pressure at a tempera ture in the range from 100 F. to 250 F. The

yolume of primary solvent used per volume of oil will likewise depend upon .the above-named factors. When using phenol, it is preferred to use from' 1 to 4 volumes of phenol per volume of oil; The proportion of primary solvent used in the pretreater will likewise vary widely and will depend upon the particular conditions of operation. When using phenol, for example, it

may bedesirablectointroduceas high as,60%

of thextotal phenol into the pretreater, although, in general, it is preferred to introduce not over 50% of the phenol into the pretreater. In general, ityis p'referred to introduce not over 20% of the total phenol into the pretreater. i l The quantity of secondary solvent used per volume of primary solvent extract being treated will depend to a large extent upon the particular primary solvent being used and the character of the oil being treated, as well as upon the secondary solventemployed. For example, when using phenol as the primary solvent and paracyclo as the secondary solvent, it is preferred to use from about /2 volume to 2 volumes of paracyclo per volume of oil being treated. TIn. processes in which distilled phenol is used in the main extraction tower to effect a final removal of the more aromatic constituents, it may be desirable to use as high as 60% phenol based upon the volume of oil being treated. However, in. general, the quantity of distilled phenol should be less than about 30% based upon the total quantity of primary solvent. Z In order to more fully demonstrate the invention, the following examples are given which shouldnot be construed as limiting the invention whatsoever.

EXAMPLE 1 TABLE 1 Gravity n A. P. I 50.0 ASTM distillation:

I. B. P .:.I. F 310 F. B. P F-.. 450 360 50% at F The pretreater tower comprised two contact stages. The first stage, received the oil feed stock, phenol solution from the oil feed stage of the main treater, and cycle oil precipitated from the second stage of the pretreater tower. The first discharged its oil phase to the main treater and discharged its phenol phase to the second stage of the pretreater. Phenolic water added to the second stage of the pretreater precipitated cycle oil which then entered the first stage as described above. The phenol solution from the second stage was distilled for the recovery of phenoland stripped pretreater extract.

'Ihe main treater comprised seven contact stages. Distilled phenol flowed countercurrently to raffinate oil in the three final stages; undistilled phenol plus the phenol solutioneffiuent from the three above-mentioned stages *flowed counter-currently to the oil feed in the next three stages. The seventh stage was fed with phenol layer from the oil feed stage and with phenolic water used to precipitate a cycle oil fraction. The cycle oil was returned to the-oil feed stage, The phenolsolution containing the TABLE 2 Main treater:

Point of introduction of distilled phenol F Point of introduction of undistilled phenol F Point of introduction of pretreated oil charge F 1.55 155 Bottom of tower F A temperature of 120 F. was maintained on the re-extraction tower. A phenol layer from the re-extraction tower was dried by flashing ofi phenolic water at an absolute pressure of 150 mms. at a temperature of 167 F. The distillate from the drier was cooled whereby layers of phenolic water, paracyclo, and phenol were obtained. The phenolic water was returned to pretreater and to the main treater in measured amounts. The paracyclo and phenol from the drier were combined with distillates of phenol and paracyclo from the raflinate and extract strippers. Rafiinate and extract oils were freed of phenol and paracyclo by distillation under vacuum. The phenol and paracyclo distillates were combined, cooled, and the resulting liquid phases separated. The distilled phenol liquid phase was dried by heating to a temperature of 170 F. at an absolute pressure of 145 mms. The recovered paracyclo and dried distilled phenol were measured and returned to the re-extraotion tower and main treater respectively. Results of this operation are summarized in the following table:

TABLE 3 Material balance Parts by Parts by volume volume charged recovered Oil feed 100 0 0 63.2 Pretreater extract. 0 10. 1 Main extract 0 26. 7 Distilled phenol... 60 61. 7 Undistilled phenol 240 227. 2 Phenolic waten. 12 8. 2 Paracyclo 120 113. 8

TABLE 4 I ntermediate streams Parts by Volume Phenol layer to pretreater 70 Paracyclo in feed to pretreater 1 Phenol-extract solution from pretreater 51.1 Main raflinate solution 98.3 Main extract to re-extraction tower 247.3 Undistilled phenol to drier 238.8 Paracyclo and main extract solution 126.6 Phenolic water to pretreater 2 Phenolicwater to main treater 10 TABLE 5 Qualzty 0 ml charge and products Raffi- Pretreater Main Charge nate extract extract Gravity, A. P. I 21. 7 26. 7 8. 3 14. 7 Open cup flash, F 390 405 395 375 Saybolt universal v 1; 100 469 296 1290 At 210 F 53. 8 49. 8 Viscosity index 36 Neutralization value... Carbon residue.... Bomb sulfur 2% hour Sligh No.. Tag Robinson col0r....

EXAMPLE 2 By way of contrast and to illustrate the improvement in product quality obtainable by use of a pretreater and main treater operating in combination, the results illustrated by Example 1 can be compared with those obtained when treating the same oil feed stock with the same quantities of reagents at the same treating temperatures in equipment diifering from that, used in Example 1 only in the omission of the two stage pretreater.

TABLE 6 Main treater:

Material balance Parts by Parts by volume volume charged recovered Oil feed 100 0 Rafiinate 0 65.6 Extract 0 34.3 Distilled phenol.... 60 54. 1 Undistilled phenol. 240 241. 5 Phenolic water....- 10 7. 3 Paracyclo 120 122. 0

TABLE 8 Intermediate streams Parts by Volume Paracyclo in feed to main treater 1 Phenol-extract solution direct to extract stripper 30 Main rafiinate solution 118.4 Main extract to re-extraction tower 256.4 Undistilled phenol to drier 255.2 Paracyclo and main extract solution 151.2

TABLE 9 Quality of oil charge and products Charge Rafiinate Extract Gravity, A. P. I 21.7 26.4 13.8 Open cup flash, F 390 Saybolt universal viscosity At 0 F 469 Tag Robinson color The significant improvement obtained by use of the pretreater in combination with the main treater is illustrated by the lower neutralization value and higher color of the rafiinate oil, as is evident from the comparison of Table 5 with Table 9. Furthermore, the results shown in Iable 5 are not to be regarded as representing the maximum diiierence between the two methods of operation, or as representing the highest product quality obtainable by use of the pretreater, inasmuch as only two contact stages were used in the pretreater, of Example 1 whereas the pretreater tower of a full scale commercial installation would contain a greater number of contact therefrom by distillation, separating said rafiinate phase and treating the same with the major proportion of the primary solvent in a secondary extraction zone, removing a raffinate phase from said secondary extraction zone and separating the solvent from the raiiinate by distillation, removing a solvent extract from said secondary extraction zone and re-extracting the same in a tertiary extraction zone with a secondary solvent having a preferential selectivity for the extract as compared tosaid primary solvent, removing primary solvent from said tertiary extraction zone and returning a minor proportion to said primary extraction zone and a major proportion to said secondary extraction zone, removing from said tertiary extraction zone a secondary solvent phase containing mineral oil extract, separating said secondary solvent from said oil extract by distillation and returning said secondary solvent to said tertiary extraction zone.

2. Process in accordance with claim 1 in which said primary solvent is selected from the class of solvents having a preferential selectivity for the more aromatic type compounds as compared to the more parafiinic type compounds and in which said secondary solvent is a solvent which has a preferential selectivity for petroleum oil compounds as compared to primary solvents.

3. Process in accordance with claim 1 in which said primary solvent is phenol and said secondary solvent is a highly pararfinic petroleum naphtha boiling in the range from about 300 F. to 400 F. and which contains minimum amounts of constituents which are soluble in said phenol at operating temperatures and pressures.

4. Process in accordance with claim 1 in which said minor proportion of primary solvent is from 20% by volume based upon the oil feed to 45% of said major proportion of primary solvent and said major proportion of primary solvent comprising from about 100% to 400% of solvent based upon the oil feed.

5. Process in accordance with claim 1 in which an anti-solvent is introduced into the primary and secondary extraction zones, said anti-solvent being secured by distillation from the primary solvent phase withdrawn from said tertiary extraction zone.

6. Improved solvent treating process comprising contacting a petroleum oil with a primary solvent phase in an initial extraction zone under conditions to form a solvent extract phase and a rafiinate phase, removing said solvent extract phase and recovering the solvent by distillation, separating said rafiinate phase and treating the same in a secondary extraction zone with the major proportion of said primary solvent, separating the raffinate from said secondary extraction zone and recovering the primary solvent therefrom by distillation, removing a minor proportion of said primary solvent phase from said secondary, extraction zone and introducing the same into said initial extraction zone, separating the solvent extract phase from said secondary zone and i e-extracting the same in a tertiary zone with a secondary solvent having a preferential selectivity for the extract as compared to said primary solvent, separating said primary solvent and returning to said secondary extraction zone, separating a secondary solvent extract phase from said tertiary zone and recovering the solvent therefrom by distillation, returning said recovered secondary solvent to said tertiary zone.

7. Process in accordance with claim 6 in which said minor proportion of said primary solvent phase is removed from said secondary extraction zone from a point adjacent to the point at which the raffinate from the initial extraction zone is introduced into said secondary extraction zone.

8. Process in accordance with claim 6 in which said primary solvent is phenol and in which secondary solvent is a highly parafiinic petroleum oil boiling in the range from about 300 F. to 450 F. and containing minimum amounts of components which are especially soluble in the phenol.

9. Process in accordance with claim 6 in which the amount of primary solvent contacted with the oil in, said initial stage is from 20% of solvent based upon the oil feed to 45% of the primary solvent introduced into said secondary extraction zone and in which the quantity of primary solvent contacted with the oil in said secondary zone is 100% to 400% of solvent based upon the oil.

10. Process'in accordance with claim 6 in which said raffinate from said secondary stage is contacted with distilled primary solvent prior to removal from said secondary zone.

GEORGE T. ATKINS, JR. 

